U.S. Navy FA-18 Hornets cram the flight deck of the USS George Washington during a joint military exercise with Japan in the Pacific Ocean near Japan’s southernmost island of Okinawa on Thursday amid heightened tensions in the region.

BEIJING — China said Thursday it had sent warplanes to patrol its newly declared maritime air defense identification zone, ratcheting up a dispute over an island chain that has turned into a dangerous standoff in the region.

The move came after Japan and South Korea said Thursday that they had sent surveillance aircraft of their own into the area. The United States has joined many of China’s neighbors in condemning its decision earlier this week to declare the area a defense identification zone and defied Beijing by flying two U.S. B-52 bombers through the area Tuesday.

A Chinese air force spokesman, Col. Shen Jinke, said several fighter jets and an early warning aircraft had been sent on “defensive” air patrols in the zone, to “strengthen the monitoring of aerial targets,” the Xinhua state news agency reported.

Experts say China’s decision to establish the zone — bolstered by a threat that any noncommercial aircraft entering it without notice could face “defensive emergency measures” — has inflamed an already tense situation with Japan and raised the possibility of military conflict.

Beijing had initially reacted calmly to the U.S. challenge on Tuesday, simply noting that it had identified and monitored the American warplanes. That muted response drew criticism from citizens on Chinese micro-blogging sites and even from state media.

The nationalist Global Times newspaper said the United States had engaged China in a “war of public opinion,” and that Beijing had “failed to make a timely and ideal response.”

“Beijing needs to reform its information release mechanism to win the psychological battles waged by Washington and Tokyo,” the paper said in an editorial.

Shen said the Chinese air force would remain on high alert and would take “relevant measures according to different air threats” to defend the country’s airspace, Xinhua reported.

In another editorial, the Global Times said Japan, not the United States, was the target of the new zone and suggested the enforcement of the zone would be selective.

“If the U.S. does not go too far, we will not target it in safeguarding our air defense zone,” the newspaper wrote. “What we should do at present is to firmly counter provocative actions from Japan.”

The latest flights intensify the game of dare being played above Asia’s contested maritime territory. Analysts said China had established the zone to bolster its claims to a chain of tiny, rocky islands administered by Japan, and to match a similar air defense identification zone long established by its rival.

But they said the decision could have backfired, uniting several of China’s neighbors in condemnation and providing the United States a perfect opportunity to demonstrate its commitment to ensuring stability in the Asia-Pacific region.

A Japanese government spokesman said Thursday that its Lockheed Martin-made turboprop patrol planes have been conducting routine flights in China’s air defense identification zone since Beijing’s declaration. The spokesman did not say specifically when the flights have taken place or how many there have been. Japan has not been notifying China of its activities.

Japan’s Defense Ministry did not confirm the flights, but one official, requesting anonymity to describe the situation, said that Japan is “conducting the same monitoring activity as before, and we will not change or restrict such activities.”

South Korea’s flight took place Wednesday near the area of a South Korean maritime research center, built atop a submerged rock that Seoul and Beijing contest.

The flight marks a “clear sign that Seoul will not recognize the new airspace claim,” South Korea’s Yonhap news agency said in its report. Yonhap also reported Thursday that China had rejected Seoul’s request to redraw its air defense identification zone and eliminate an overlap with the zone of South Korea. The South in turn said it may expand its own zone.

In Asia’s waters, territorial disputes go back decades or centuries and draw in nearly every nation in the region. The nastiest dispute of late has been between Japan and China over several uninhabited islets and rocks known as the Senkaku in Japanese and the Diaoyu in Chinese.

Japan infuriated China last year by purchasing several of those islets from a private landowner, and China has since increased its surveillance — both with vessels and aircraft — around those islands. Japan has frequently scrambled its own fighter jets in response.

U.S. officials said China’s unilaterally announced air defense identification zone needlessly raised tensions between Asia’s two largest economies.

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